The role of the chromospheric magnetic canopy in the formation of a sunspot penumbra

Abstract

While it is being conjectured that a chromospheric canopy plays a role in penumbra formation, it has been difficult to find observational evidence of the connectivity between the photosphere and the chromosphere. We investigate the existence of a chromospheric canopy as a necessary condition for the formation of a penumbra and aim to find the origin of the inclined magnetic fields. Spectropolarimetric observations of NOAA AR 12776 from the GRIS@GREGOR instrument were analyzed. Atmospheric parameters were obtained from the deep photospheric Ca I 10839 Å line (VFISV inversion code), the mostly photospheric Si I 10827 Å line (SIR inversion code) and the chromospheric He I 10830 Å triplet (HAZEL inversion code). In the deepest atmospheric layers, we find that the magnetic properties (inclination and field strength distribution) measured on the sunspot sector with fully fledged penumbra are similar to those measured on the sector without penumbra. Yet, in higher layers, magnetic properties are different. In the region showing no penumbra, almost vertical chromospheric magnetic fields are observed. Additionally, thin filamentary structures with a maximum width of 0.1 arcsec are seen in photospheric high-resolution TiO-band images in this region. The existence of a penumbra is found to be discriminated by the conditions in the chromosphere. This indicates that a chromospheric canopy is a necessary condition for the formation of a penumbra. However, our results demonstrate that inclined fields in the chromospheric canopy are not needed for the development of inclined fields in the photosphere. We question the `fallen-magnetic-flux-tubes' penumbra formation scenario and favor a scenario, in which inclined fields emerge from below the surface and are blocked by the overlying chromospheric canopy.

arXiv commentAccepted by Astronomy & Astrophysics on 11/03/2023

References in corpus (34)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: SHARPs -- Space-weather HMI Active Region Patches
• The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance
• CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
• VFISV: Very Fast Inversion of the Stokes Vector for the Helioseismic and Magnetic Imager
• Advanced Forward Modeling and Inversion of Stokes Profiles Resulting from the Joint Action of the Hanle and Zeeman Effects
• Numerical sunspot models: Robustness of photospheric velocity and magnetic field structure
• Penumbral fine structure and driving mechanisms of large-scale flows in simulated sunspots
• An active region filament studied simultaneously in the chromosphere and photosphere: I - Magnetic structure
• Structure of sunspot penumbral filaments: a remarkable uniformity of properties
• The formation of sunspot penumbra. I. Magnetic field properties
• Convective blueshifts in the solar atmosphere: III. High-accuracy observations of spectral lines in the visible
• Precursor of Sunspot Penumbral Formation discovered with Hinode SOT Observations
• The role of emerging bipoles in the formation of a sunspot penumbra
• Deep probing of the photospheric sunspot penumbra: no evidence for magnetic field-free gaps
• An active region filament studied simultaneously in the chromosphere and photosphere. II. Doppler velocities
• Height variation of the cutoff frequency in a sunspot umbra
• Formation of the penumbra and start of the Evershed flow
• GREGOR: Optics Redesign and Updates from 2018-2020
• Small-scale magnetic flux emergence in the quiet Sun
• Spectropolarimetric analysis of an active region filament. I. Magnetic and dynamical properties from single component inversions
• On the formation of a stable penumbra in a region of flux emergence in the Sun
• Photospheric Signatures of Granular-scale Flux Emergence and Cancellation at the Penumbral Boundary
• The problem of the height dependence of magnetic fields in sunspots
• Absolute velocity measurements in sunspot umbrae
• Three-dimensional magnetic structure of a sunspot: comparison of the photosphere and upper chromosphere
• Height variation of magnetic field and plasma flows in isolated bright points
• Height dependence of the penumbral fine-scale structure in the inner solar atmosphere
• Spectropolarimetric analysis of an active region filament. II. Evidence of the limitations of a single component model
• Capabilities of bisector analysis of the Si I 10827 A line for estimating line-of-sight velocities in the quiet Sun
• Temporal Evolution of the Inverse Evershed Flow
• Penumbral decay observed in active region NOAA 12585
• The pre-penumbral magnetic canopy in the solar atmosphere
• The formation and decay of sunspot penumbra in Active Region NOAA 12673

Cited by in corpus (6)

• Onset of penumbra formation
• Magnetic field fluctuations in the shocked umbral chromosphere
• Magnetic properties of orphan penumbrae
• Decay of a photospheric transient filament at the boundary of a pore and the chromospheric response
• Sunspot simulations with MURaM -- I. Parameter study using potential field initial conditions
• The dependence of the magnetism of a near-limb sunspot on height